Set default documents

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare the write profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false), so the safety picture is covered. The description adds useful domain context that this affects how nginx resolves directory index requests, but omits whether the change is immediately live or requires a reload, and what happens to the previous index list.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single tight sentence with the action front-loaded, no filler. The trailing 'comma separated' is slightly redundant with the schema but costs little.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With annotations covering the write profile and a fully described schema, the definition is minimally viable, but for a config-mutating tool it should at least indicate that the site id must reference an existing site and whether a reload/restart is implied.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% with both parameters fully described, so the schema already carries the semantics. The description only restates the comma-separated format already present in the Index parameter description, adding no new format or validation detail.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb ('Change') and resource (nginx directory index filenames), which tells an agent exactly what the tool mutates. It is distinguishable from read-only siblings like site_get_config or site_get_rewrite, though it never names a specific alternative it could be confused with.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no guidance on when to use this versus siblings such as site_set_rewrite or site_set_run_path, nor any prerequisite (e.g. that the site must already exist, or that nginx may need a reload). The agent must infer usage entirely.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.